POV display

POV display

A "persistence of vision display" (POV display) has only a single line of LEDs blinking on and off.
The display mechanically sweeps it across a person's field of view,
giving the illusion of a 2D display.

(Do I need a diagram or a picture here?)

(Nearly all LED displays in microwave ovens and alarm clocks electrically sweep the digits across a person's field of view, giving the illusion that it's displaying all 4 digits of the time "12:55" when actually only one digit is illuminated at any one instant).

Do you know what the difference is? Does your flashlight really
produce 10 times the light ( in lumens)? Or does the flashlight merely
focus its light on a tiny spot, so that that spot gets 10 times as
many candelas ?

From the mcd rating, it appears that the first one is more than 2wice
as bright -- and it is, if you're directly in front of it when you
look at it.
However, if you're even the tiniest bit off-center, the second one is
much brighter -- in fact, the total lumens that second LED puts out
(2500 mlm) is slightly more than the total lumens than the first one.
If you diffuse the light and try to light up a whole room with an
array of them, the second one will make the room brighter.

$2.550 Lumex "DSP LED" 67-1876-ND: blue, 5 mm, 2500 mcd ( DigiKey ) apparently have some kind of internal chip. All colors run at 2.0 V nominal (1.5 V minimum) (rather than running on current like most LEDs. unfortunately, the data sheet doesn't suggest how much current they take -- I presume more than 20 mA).

The Orbital Rendersphere displays images and videos on a four-foot diameter spherical surface using persistence of vision (POV).
Uses a (stationary) Mac Mini to render each frame, and a (spinning) BeagleBone Black to update the LEDs.
Slip ring for power; Wi-Fi to transfer data.
The Orbital Rendersphere displays video at 30 frames per second by spinning four vertical LED strips spaced 90 degrees apart at 450 RPM.
36 feet of WS80211 LED strips.
(But it looks like 2 complete circles, each 4 ft diameter -- isn't that closer to 25 feet?)
102x224 pixel resolution.
Several people comment that this is the biggest POV globe they've ever seen.
It's mentioned on p. 1-44 of
John Baichtal, "Robot Builder"[9].
Uses LEDscape[10].

Mike Szczys. "Full-color video on a spinning POV display". Built by Félix, Sylvain, and Jérémy at at Telecom ParisTech. highest-resolution POV display I've seen so far. "The time it took us was roughly two months full time". (Does this have a name?)

"Borg Ventilator". Twice the resolution of the Telecom ParisTech display? A total of 244 RGB LEDs (spread over 4 wings). Has standard VGA input; a Xilinx FPGA and a bunch of support chips convert to circular coordinates. Power through slip rings. Data through non-contact inductive transfer (recycled VCR head). "The speed is infinitely adjustable between 0 and 2500 rpm / min. The FPGA adapts to the actual speed"

Mentions
<q>
"we recently decided to move this project to the Raspberry Pi board away from Arduino.
The capabilities and processing power of the Pi are much greater than Arduino.
... [but] ... the refresh rate is too slow, much slower then the Arduino was.
We need some help figuring out how to turn up the SPI speed with our current software arrangement.
...
used Phillip Burgess' at Adafruit 'Light Painting' Python script to process images and output to the LPD8806 http://learn.adafruit.com/light-painting-with-raspberry-pi/software
"</q>

Bicycle LED POV is an electronic LED bar to attach on bicycle wheels. When riding the bicycle, the LED bar will draw with light, text messages and image animations. Free/Open hardware, firmware and software.

"luscious electric delight": source and schematics for a large graphical LED panel. Uses 12 MAX6953 LED drivers; each MAX6953 drives four 5x7 led matrices. The PC generates arbitrary bitmap, sends it out the serial port to a PIC, which translates it to I2C bus connected to all the MAX6953 LED drivers, which update the image at a continuous frame rate of 30fps.

Sunrise LED Alarm Clock ATMega8515 controlling two color-mixed high-power LED channels with PWM. Also contains a RTC circuit and a serial port. Full source including PC Windows serial port communication code.

"Mechanically Scanned LED display" by Chris "thekeeser". Using PIC16F628, a infrared 1 pulse per revolution sensor so it can automatically adapt to any rotation rate, and multi-colored LEDs. Detailed notes on the software development.

It might be nice to make a spinning electronics page to describe the many weird and wonderful ways that people (a) get power to the spinning electronics, and (b) transmit data to and from the spinning electronics.
POV displays are the most popular kind of spinning electronics,
but the same approaches are useful for other kinds of spinning electronics
such as run-time tire pressure sensors and bioreactors.